This invention relates generally to monitoring waveguide birefringence.
Birefringence is the difference in refractive indexes along the X and Y axes of a waveguide. In order to characterize a waveguide, such as a planar waveguide, it is desirable to know its birefringence. Currently there is no test equipment known to the inventors that can directly monitor waveguide birefringence.
Birefringence, for example, causes polarization-mode dispersion. Polarization-mode dispersion is pulse spreading caused by a change of waveguide polarization properties. This is a random dispersion that is difficult to compensate for. In order to describe the polarization-mode dispersion, it is necessary to determine the birefringence.
Generally, any type of unintended dispersion is undesirable since it changes the characteristics of a light pulse. Thus, to some degree, it is desirable to either avoid or compensate for such dispersion. In the case of polarization-mode dispersion, in order to compensate or avoid the dispersion, it is first desirable to characterize that dispersion.
A birefringence contribution may add to polarization dependent loss (PDL) in planar light wave circuits based on optical interference. This may become an issue, for example, in arrayed waveguides and Mach-Zehnder interferometers.
Thus, there is a need for a way to directly characterize the birefringence of a waveguide.